1. Field of the Invention
The present invention relates to optical reflectors and methods for producing the same.
2. Background of the Art
Special light reflectant surfaces are used in a variety of applications requiring light energy to be close to completely reflected while providing an even distribution of light from the surface. While good-mirrored surfaces can provide nearly perfect reflectivity of visible light, the light energy exiting these surfaces does so only at an angle equal to the incident angle of light contact. For many applications it is important that light be reflected with an even distribution of light from the surface. This latter property is referred to as diffuse or “Lambertian” reflectance.
In one application, laser or integrating cavities are being made with diffusely reflecting material. Diffusely reflecting material is preferably used in laser cavity applications to more uniformly spread energy from the flash lamp or other exciting means into the lasing material. A diffuse reflecting medium has the advantage of not limiting a laser cavity to a shape with focal points, opening the field to new laser cavity configurations.
The requirement for a highly efficient laser having a cavity made of diffusely reflecting material has resulted in the “Kigre” cavity which is a cavity defined by a glass layer formed over barium sulfate and which generally results in a 97% diffuse reflectivity. It has been found that such cavities degrade quickly over time and usage, usually by yellowing. Cavities have been made of a gold or silver coating. However, these cavities have resulted in only 94% to 95% specular reflectivity.
Materials commonly used as a diffuse reflector include a polyester material or a polytetrafluoroethylene (PTFE) material. One such PTFE material is Spectralon®, by Labsphere, which reports the highest diffuse reflectivity. It is made of the same material as in Teflon®, and the material is processed carefully to optimize its diffuse reflectivity. Unfortunately, such PTFE based material degrades under exposure to ultraviolet light. Additionally, such PTFE based materials do not retain the same diffuse reflectivity properties in the ultraviolet range as in other wavelength ranges, and thereby limit the applications. Additionally, such PTFE films have been observed to have less than the desired diffuse reflectivity for current and future optical applications.
Therefore, there is a need for developing materials and structures from such materials with improved diffuse reflectivity.